The invention relates to a method of obtaining a three-dimensional deformation of an organ which is deformable over time and extends in a three-dimensional space using at least two sets of data representing points on said organ and corresponding to distinct times in the deformation of the organ. This invention also relates to an apparatus for implementing the method described above.
The invention finds its application in the field of the processing of medical images. Many acquisition methods can in fact benefit from the application of the method according to the invention provided that, between two acquisitions of the organ, points on a first acquisition can be matched with points on a second acquisition. Thus, using known readjustment algorithms, the method can be used for images obtained by ultrasonic, radiological or magnetic resonance techniques. In particular the organ images marked by spatial magnetic resonance modulation make it possible to obtain the deformation of an organ on an acquisition plane very faithfully. This is because this marking is visible on the images in the form of marking lines with points of intersection. The marking lines deform while following the deformation of the organ. Said points of intersection are then chosen as points for which a correspondence is known.
A method of obtaining the three-dimensional deformation of an organ is already known in the state of the art through the publication by Park et al. entitled “Analysis of left ventricular motion based on volumetric deformable models and MRI-SPAMM”, Medical Image Analysis 1(1): 53–71 (1996). In this document, Park proposes a method of reconstructing the three-dimensional movement of the left ventricle of the heart using data marked by spatial magnetic resonance modulation. The technique presented uses parameterized volumes whose parameters are to be determined as a function of the marked data. To use parameterized volumes, it is necessary to make a first convergence of a mesh model governed by mechanical laws, the image data producing forces, to determine the boundaries of the organ and then make an optimized approximation of the deformation of the mesh with respect to the positions of the tags. The calculations generated by this method are complex and, consequently, the method is difficult to automate in real time. Moreover, the deformation parameters are calculated once the second deformation convergence of the mesh has been carried out and this causes propagations of errors at each calculation step.
One object of the invention is to provide a method of quantifying the deformation of the organ with very good precision and with simplified calculations which make it possible to carry out a study in real time. The latter property is essential for the clinical usage of a determination of a three-dimensional movement.